1. Field of the Invention
The present invention relates generally to echo cancellers, and more specifically to a multi-channel echo canceller for a teleconferencing system and the like.
2Description of the Related Art
A multi-channel echo canceller is described in a paper "Compact Multi-channel Echo Canceller with a Single Adaptive Filter Per Channel", Akihiro Hirano et al, Proceedings of the 1992 IEEE International Symposium on Circuits and Systems, San Diego, Calif. May 10-13, 1992. This paper addresses to the convergence problem that is associated with adaptive filter coefficients when received signals have strong cross-correlation. The known echo canceller is provided with a single set of filter coefficients to reduce acoustic echoes at the near and far ends of the system as well as transmission echoes by taking into account all possible microphone-loudspeaker combinations at the near end and all possible acoustic paths from a talker to microphones at the far end. The known echo canceller estimates an inter-channel time difference between the propagation delays of the received signals and couples one of the signals having a smaller propagation delay to the adaptive filters to produce an echo replica from each adaptive filter. The echo replica is subtracted from a corresponding signal to cancel the echo contained therein. The adaptive filters are controlled with residual echoes so that they reduce to a minimum. The filter coefficients of each adaptive filter define a transfer function that is converged to an optimum value for a particular talker at the far end in response to the selected signal. Therefore, the transfer function of each adaptive filter tends to offset from the optimum value in response to a talker's movement. However, there is a noticeable amount of delays in the adaptive filters for adapting to the changing acoustic parameters at the far end.